FIG. 7 is a schematic diagram of a plant having a gas turbine combustor which is subjected to steam cooling, in a combined plant in which a gas turbine and a steam turbine are combined. In the figure, a combustion gas 7, which is created as a result of power generation in gas turbine 1 and is discharged, is supplied to the boiler 4, and in boiler 4, steam 9 is generated by this high-temperature combustion gas 7 from the gas turbine 1, and the exhaust gas 50 is discharged to the atmosphere from smokestack 51. The steam 9, which is generated in the boiler 4, is supplied to steam turbine 5, and this turns a power generator, so that electric power is obtained. The cooling of the combustor of gas turbine 1 is conducted by extracting a portion of the steam produced by boiler 4 and conveying this steam 40 to the combustor, and the steam heated during this cooling process as recovered steam 41 is then reused by being returned to steam turbine 5.
Next, the control of the steam cooling for the gas turbine combustor in a combined plant having the structure described above will be explained.
FIG. 6 is a schematic flow diagram of a steamcooling system for gas turbine combustors in a conventional combined plant. In the figure, controller 2 controls the flow of the steam, while combustion gas from the gas turbine 1 is led to the boiler 4, which generates steam. Furthermore, this steam-cooling system is provided with an auxiliary steam source 3, a steam turbine 5, and a condenser 6. Steam recovery valve 11 is provided in the recovered steam flow path 61 from the outlet of the combustor of gas turbine 1. Furthermore, steam valve 12 is provided in extracted steam flow path 62 from the boiler 4 to the inlet of the combustor of gas turbine 1. Auxiliary steam valve 13 is provided in flow path 63 in order to introduce the steam from the auxiliary steam source 3 into the flow path 62 leading to the inlet of the combustor of gas turbine 1. The opening and closing of these valves 11 through 13 is controlled by the controller 2.
Furthermore, a temperature sensor 21, which detects the temperature of the steam flowing through the auxiliary steam flow path 63, a temperature sensor 22, which detects the temperature of the steam flowing into the inlet of the combustor of gas turbine 1, and a temperature sensor 31, which measures the temperature of the steam at the outlet of the combustor of gas turbine 1, are provided in the system, and the detected values detected by these temperature sensors are input into controller 2. In addition to the parts described above, an actual plant would be provided with a drain exhaust system, opening and closing valves, flow rate and pressure adjustment valves, pressure detectors, and the like; however, as these are not required for an explanation of the technological background of the present invention, an explanation thereof will be omitted here.
In a control system such as that described above, prior to supplying steam to the combustor of the gas turbine 1, the warming of the piping systems, and the discharge of the drain during operation, are conducted; however, those systems are omitted from the figures. Prior to starting, the auxiliary steam valve 13 is first opened, and auxiliary steam is allowed to flow into the auxiliary steam flow path 63 from auxiliary steam source 3, and this flows through the combustor of gas turbine 1 via flow path 62, and is discharged via a flush pipe which is not depicted in the figure, so that a warming up is conducted. Next, gas turbine 1 is started, and after a predetermined period of time, the auxiliary steam valve 13 is closed, while steam valve 12 and steam recovery valve 11 are opened, the steam extracted from the boiler 4 is supplied to the combustor of gas turbine 1, and the combustor is cooled using this steam, while the steam heated in the process of cooling is returned to steam turbine 5 and reused. The amount of cooling steam supplied to the combustor of gas turbine 1 is adjusted to the amount necessary for the gas turbine load by conducting programmed control in the controller 2.
As described above, when the signals of temperature sensors 21, 22, and 31 are input into the controller 2, the opening and closing of the auxiliary steam valve 13, the steam valve 12, and the steam recovery valve 11 is conducted in accordance with a program predetermined, and steam cooling is conducted so that the combustor of gas turbine 1 remains at planned temperatures from the starting of the gas turbine and throughout the operation thereof.
As described above, in conventional steam-cooling systems for gas turbine combustors in combined plants, the combustor is cooled using steam extracted from a boiler, and after it has been used for cooling, the steam is returned to the steam turbine as recovered steam, and the required amount of steam is controlled by a controller using a program determined in advance in accordance with the load on the gas turbine. However, during the starting in the plant, and during periods of load change, delays occur in response to the temperature and pressure of the steam generated at the boiler, and as a result of these delays, the steam employed for cooling the combustor is insufficient, so that there are cases in which the steam temperature in the flow path on the cooling steam outlet side of the combustor increases, and exceeds planned temperatures, so that the temperature of the combustor increases excessively. Furthermore, in order to counteract this insufficiency in the steam employed for cooling the combustor, it was necessary to increase the size of the boiler.